The invention relates to an apparatus for laying a pipeline in water, comprising a vessel with means for assembling a pipeline from pipe parts, an elongate curved guide body arranged on the hull of the vessel for guiding the pipeline from the vessel into the water, and means for carrying the guide body into respectively out of the water.
Depending on the pipe diameter, such an apparatus is suitable for laying a pipeline to a certain depth, for instance about 1.5 km at a pipe diameter of 300 mm. When a pipeline is laid at greater depth with such an apparatus the loads on the hull become too great. These loads consist mainly of static vertical forces of the magnitude of the submerged weight of that part of the pipeline situated between the vessel and the bed of the water, and the dynamic forces which occur due to the swell of the waves. Already known is a body consisting of pivoting joints for the purpose of compensating the above forces, but it is not easily possible therein to properly control the bending radius of the pipeline at the position of the guide body, whereby, depending on the conditions, plastic deformation of the pipe occurs.
The object of the present invention is to provide an apparatus of the above described type wherein the above stated drawbacks are obviated.
The advantage of an apparatus according to the invention is that when the box-like body takes an air and watertight form the guide body acquires a buoyancy, whereby a part of the forces exerted by the pipeline is absorbed by the guide body and the load on the hull is reduced. The closed, fixed guide surface formed by the box form also better supports the pipeline lying on roller supports.
An embodiment according to the invention comprises a box-like body which in any cross-section has a small width relative to the height. The hydrodynamic forces are hereby minimal, while the box-like body is sufficiently strong to absorb the substantially vertical pipeline forces and vessel movements.
In a further embodiment according to the invention the guide body comprises a curved guide surface formed from pipe supporting elements, preferably rollers, which rollers are arranged at a mutual distance such that the greatest bending of the pipe takes place at the position of the rollers, wherein the bending is acceptable in terms of safety and design provisions.
A further embodiment according to the invention comprises a rod-like member which is arranged hingedly on the hull and carries the box-like body in respectively out of the water and which extends between a point on the vessel and a point on the box-like body at a distance from the hinge. This rod carries the box-like body out of the water in the case of bad weather conditions or in the case of transport, and carries the box-like body into the water for laying of a pipeline, wherein depending on the resultant force it exerts a tensile force or pressure force on the box-like body.
Another embodiment according to the invention comprises a box-like body in air and watertight form which is provided with one or more closed spaces for receiving ballast. It is hereby possible to regulate the excess or lack of buoyancy in particular cases by receiving for instance water in the spaces or pumping it therefrom.
Various aspects will be further elucidated with reference to the drawings of a preferred embodiment.